Emergency communication system, particularly for mines



g'Aug. 28; 1951 N. F. AGNEW 2,556,106

EMERGENCY COMMUNICATION SYSTEM PARTICULARLY FOR MINES Filed Dec. 9; 1947 INVENTOR NORMAN F. AGNEW Patented Aug. 28, 1951 TKRTIGULARLY FOR MINES Norman F -Agnew, Penn Township, Allegheny gounty, Pa., assignor to Farmers Engineering a Manui'agturiiig (30., Bittsburg h, 2a., a partne m sons wmaia P. Place 11E of Norman F. Agnew and itiiplicationD'ecemlier 9, I947, Serial No. 790,489

4 claims.

This invention relates to a communication system for installation in conjunction with an electric railway. It is particularly adapted for providing emergency service in mines.

Until recently, there has been no improvement in mine communication systems for many years. Conventional telephone systems have been used extensively but are subject to the difflculty of reaching fixed points underground and the dangers of circuit interruptionpaused by slate falls, the telephone wire being the most fragile conductor in the mine. While carrier-current systems using the railand trolley of the electric railway usually installed in inines were tried several years ago, they were not successful because of the noise created by the motors of loco- .motives and auxiliaries, until frequency-modulation was adopted recently. Such systems are now operating very satisfactorily utili'z'ing' direct current from the same source which supplies the railway, but are rendered useless by failure of the normal power supply. Standby batteries could be employed as an emergency power supply but they would be costly Because of the amount of power required. As a 'ies'ulhit has been the practice, where frequency-modulated carrier-current has been used for cerium communication to provide an ordinary telephone system for emergency service. in 'oi'defto comply with safety requirements, despite the considerable cost thereof and the danger of "famine because of circuit interruption inejfitioned above. My invention provides emeiency communication in mines without the necessity of special telephone circuits, thereby eliminating the cost and maintenancethereof as' 'well as the everpresent hazard of breakage. a referr'ea embodiment, I employ emergency telephone equipment connected to the railway circuit consisting of the trolley and rails of the minefhaiilin'g system for use when the power supply has failed or been disconnected. Such equipment includes a'novel transmitter-receiver including an amplifier and a single switch therefor whereby 'incoming signals are delivered by an eiect'ro-"magnetic speaker and the latter s'erv'es ass "inic'rophone on operation of the switch for picking up and transmitting words spoken thereint'o. Preferably a complete transmitter-receiver unit with local battery is located outside the mine and at I one or more points within the mine. The units are capaeitively connected to the'trolley or other feeders. Each mine locomotive 'is preferably vl'p'iovided with a; receiver capacitively cofiriected to h ey P rmitting 1 fi fifiifi 311% 190 receive instructions from any transmitterreceiver. The emergency equipment cannot be used when power is on the railway trolley because of the noise existing as aforesaid but, as soon as the power supply fails or is disconnected, the emergency equipment is ready for use, this being made possible by elimination of the noise as a result of stoppage of the motors connected to the power circuit supplying the locomotives and auxiliaries as well. I r

A complete understanding of theinvention may be obtained from the following detailed description and explanation which refer to the accompanying drawings. In the drawings,

Figure 1 shows diagrammatically the general arrangement of a form of my invention which is suitable for use in a mine; and

Figure -2 is a circuit diagram of the transmitter-receiver. 7

Referring in detail to the drawings, and for the present to Figure 1, an electric railway such as that usually installed in a nine comprises a trolley or other feeder l0 and rails I l on which haulage locomotives such as that indicated at [2 travel. Power is supplied to the trolley a generator 13 or other power source through a main circuit breaker l4. At the outside office i5 is located a frequency-modulated carrier-cunrent transmitter-receiver l6 operated by power from trolley 6 for communication While the power is on. Each "mine locomotive is equipped with a similar transmitter-'ieceive'r H. such 'a transmitter-receiver i's describedfif fa "copending patent application Serial No. 713,252, 'filed Noye'rnber 30, I946, now abandoned, by Willard .1. Place.

An emergency battery-operated transmitterreceiver IB is also located in the 'office i5 and a similar unit [9 at one "or more -points in the mine. The locomotive 12 has an ordinary tersphone receiver 20 connected to the trolley through a capacity 2| which enables the driver to hear from both the transmitter-receive units is and 19. Additional receivers '22 may be installed at the working face and connected to thetrolley through capacitors 23.

The transmitter-receivers T6 and I! are employed for normal communication While the power is on the trolley III. In "case of failure of the power source [3 or opening of the circuit breaker M, the units l8 and I9 provide cornrnuiiic'ation between the oflic'e I5 and various points inside the liiin, utilizing the "'pO'w'er circuit while it is out service for normal operations.

Fleur e2 shows the detains fif'tlo'e transmittercontained unit for sending and receiving audio signals over the trolley and rail circuit H), II. The case has a handle for convenient carrying and the apparatus needs only to be connected to the trolley and ground to be ready for use. The connection to the trolley is made through a l ampere fuse 23, condenser 21, the upper back contact of a push-button switch 28, a resistor 29 and a volume-control resistor 30 to the grid of a double triode (1J6) amplifier tube 3|.

Audio signals coming in over the trolley wire are thus amplified through the first section of the tube 3|, which is resistance-coupled through capacity 32 and resistor 33 to the second section of this tube for further amplification. The output of this second section is delivered by a plate-togrid interstage transformer 34 to the grids of the two sections of a second amplifier tube 35 similar to tube 3!. This provides push-pull driving of the grids of the second tube. An output transformer 36 has its primary connected for pushpull operation across the plates of the second tube 35. The secondary of the output transformer is connected to the loudspeaker 25 through asecond back contact of the switch 28.

When the switch 23 is operated, the loudspeaker 25 becomes a microphone delivering signals through its lower front contact into the grid of a pre-amplifier tetrode tube 31 (1N5-G). Operation of the switch also transfers the outputtransformer secondary from the speaker to the trolley ID. The grid of the first amplifier tube 3| instead of being driven from the signal on the trolley wire as before, is then driven from the plate circuit of the preamplifier tube 31. In this manner, sound impinging on the loudspeaker is amplified through the tubes 3| and 35 in the same way that signals from the trolley 10 were amplified when receiving. Since the secondary of the output transformer is connected to the trolley, audio signals are impressed between the trolley and ground.

A single switch 38 in series with the filamentsupply battery 39 is used for turning the unit on and off. There is no switch in circuit with the 3" battery 40 because, when the tube elements are cold, no plate current will fiow. A neon lamp 4| placed across the primary of the output transformer 36 provides a means for testing both the A and B batteries in the unit. With the switch 38 turned on to energize thetube filaments, there is sufficient tube voltage developed when talking into the loudspeaker with the switch 28 operated, to energize the lamp to visible condition.

It will be apparent from the foregoing that the invention provides an emergency communication system for mines having several important advantages. In the first place, no special communication circuitis required since the power circuit is used for communication when out of service for power transmission. This circuit is the sturdiest physically of all those in the mine, is less subject to interruption by slate falls and is normally maintained in good working order at all times for the purpose of transmitting power. Reliability is thus practically assured. The cost I of a system according to my invention is much less than that of a, conventional telephone system with its own circuit, in one instance less than one-tenth as great. The battery power required for operation is small and the transmitter-receiver units may be made self-contained and readily portable.

Although I have disclosed a preferred embodiment of my invention, it will be understood that changes in the details shown may be made without departing from the spirit of the invention or the scope of the appended claims.

I'claim:

l. Anaudio frequency receiver and transmitter adapted to be coupled to two conductors comprising-a coupler for coupling the receiver and transmitter to one of the conductors for voice transmission, several stages of amplification said stages having, a tube having a grid as the first stage of amplification and another tube having a grid as an intermediate stage of amplification, a loudspeaker, and two circuits selectively controlled by a multipole switch by completing the following'connectionsz for receiving, connecting the coupler to the grid of the tube in the intermediate stage of amplification and the loudspeaker to the output of the last stageof amplification and for sending, connecting the coupler to the output of the last stage of amplification andthe loudspeaker to the grid of the tube in the first stage of amplification.

2. An audio frequency receiverand transmitter as describedin claim 1 in which the last stage of amplification includes an output transformer and a neon lamp connected across the primary of the transformer.

3. A communication system for mines having an electric railway includi'ng power lines, said system comprising a carrier current communication circuit connected to said power lines for power and for signal transmission and an audio frequency receiver and transmitter having a separate source of power adapted to be coupled to said power lines for voice transmission, said audio frequency receiver and transmitter also having at least three stages of amplification, a power output transformer, a loudspeaker, and leads controlledby switching means for establishingseparate circuits for receiving and for transmitting as follows: for receiving, connecting the loudspeaker to the output of the transformer and coupling an intermediate amplification stage to said conductors, for sending, connecting the loudspeaker to the first stage of amplification and coupling the transformer output to said conductors.

4. A communication system for mines havin an electric railway including power lines, said I system comprising a carrier current communication circuit connected to said power lines for power and for signal transmission and an audio frequency receiver 7 and transmitter having a separate source of power adapted to be coupled- ,to said power lines for voice transmission, several stages of amplification said stages having a tube having a grid as the first stage of amplification and another tube having a grid as an intermediate stage of amplification, a loudspeaker, and

two circuits selectively controlled by a multipole switch by completing the following connections: for receiving, connecting the coupler to the grid of the tube in the intermediate stage of amplification and the loudspeaker to the output of the last: stage of amplification and for sending, connecting the coupler to the output of the last stage of amplification and the loudspeaker to the grid of the tube in the first stage of amplificatlon.

NORMAN F. AGNEW.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Kitsee Aug. 2, 1904 Linda Nov. 5, 1912 Reineke June 2, 1914 Konn Sept. 1, 1931 Dietze May 31, 1932 Rowe Nov. 1, 1932 Frazier Sept. 22, 1936 Number 6 Name Date Bossart Dec. 15, 1936 Monk Nov. 15, 1938 Sadowsky Jan. 3, 1939 Vroom May 28, 1940 Root Sept. 17, 1940 Campbell Jan. 6, 1942 Atkinson Feb. 15, 1944 Long May 29, 1945 Brown July 30, 1946 Lang Nov. 11, 1947 Hugh Nov. 9, 1948 OTHER REFERENCES Radio and Television News, August 1949, pp. 23-25, 120. 

